Re: 1kHz 130dB distortion sinewave oscillator.

On 1/02/2025 4:37 pm, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vnka4g$3ut8i$1@dont-email.me...

On 1/02/2025 1:34 pm, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vnim5i$3hnrj$1@dont-email.me...

On 31/01/2025 5:47 am, Edward Rawde wrote:

Approaching 130dB now. Any suggestions for improvement?
It wouldn't be hard to add another four rectifier phases but then I'd have more components than Bill.

But at least I know what mine are doing.
>

This circuit was simulated in LTSpice 24.1.1 with all component updates as of 30th January 2025.
>
Take a sample near 20s and FFT on current zoom extent with Blackman-Harris window.
It's approaching 130dB at 2kHz and approaching 140dB everywhere else.
>
I do not know why C13/R28 and similar are needed but without them the simulation speed goes down to us/s
It appears that LT1115 doesn't like being simulated with very little load on its output.
Whether or not that's true in reality I've no idea and it may not be the case in earlier versions of LTSpice.
>
Simulation speed in 24.1.1 appears to be about twice as fast as earlier versions for this circuit.

>
This is a strange circuit.

>
It's also way more complex than it need be. Please see my most recent post.
I think you'll find the FET is operating conventionally. Roughly at the centre of its range when I last checked.
>

One problem with using an N-channel junction fet like J113 is that if you bias the gate at a higher voltage than the source or
drain, it acts as a diode and feeds current into the channel.
>
I've downloaded and run the second version of the simulation, and the gate doesn't seem to end up more negative than the source
or
drain.
>
It takes quite a lot of simulation time before the circuit starts acting as if were an amplitude controlled oscillator, and I'm
not interested enough to try and work how it is actually working.

>
I've modified the circuit to make sure that FET gate doesn't get forward-biased.

 Why does it matter if the FET gate is forward biased during the first 10ms Bill?
That isn't going to make the FET explode is it?
 

>
As John May pointed out a long time ago, the J113 isn't a great choice for the application.

 Did he say why?
   I've swapped in a J111. The integrator around U6

isn't well designed, and I've deleted a redundant resistor and added a huge damping resistor (R4). It means that there's a lot of
1kHz ripple on the gate voltage, and loads of harmonic content on the output - 2kHz is only 25dB below the fundamental.

 Sorry bill but I don't get why you would sabotage the circuit like that.

You aren't a quick study.

Getting a low ripple rectified output to feed into the integrator isn't a trivial task. It's part of a negative feedback control
problem which you seem to be reluctant to recognise.

 Please see the most recent circuit I posted.
It doesn't bother with DC stabilization circuits but it does do 133dB down on harmonics with pretty much nothing at 2kHz at all.

Perhaps if you measure the distortion only when the stabilisation circuit isn't feeding anything into the integrator wrapped around U6.
The current feed to set the output level by balancing out  the inputs from the rectifiers was feeding in current when it should have been sucking it out, so it wasn't a well thought-out design.
Here's a version of that circuit  which does work sensibly, even if the harmonic content of the output is only about 60DB below the fundamental.
--
Bill Sloman, Sydney
Version 4
SHEET 1 3828 932
WIRE 976 -816 816 -816
WIRE 1056 -816 1056 -848
WIRE 880 -752 880 -768
WIRE 976 -736 976 -816
WIRE 976 -736 912 -736
WIRE 816 -720 816 -816
WIRE 816 -720 720 -720
WIRE 848 -720 816 -720
WIRE 1056 -704 1056 -736
WIRE 1056 -704 912 -704
WIRE 288 -672 256 -672
WIRE 384 -672 352 -672
WIRE 480 -672 464 -672
WIRE 720 -672 720 -720
WIRE 1056 -672 1056 -704
WIRE 1168 -672 1056 -672
WIRE 880 -656 880 -688
WIRE 1056 -656 1056 -672
WIRE 1168 -640 1168 -672
WIRE 1056 -544 1056 -576
WIRE 1168 -544 1168 -576
WIRE -192 -480 -192 -512
WIRE 384 -464 384 -480
WIRE 480 -448 480 -672
WIRE 480 -448 416 -448
WIRE 576 -448 480 -448
WIRE 640 -448 576 -448
WIRE 720 -448 720 -592
WIRE 720 -448 640 -448
WIRE 1056 -448 720 -448
WIRE 1168 -448 1056 -448
WIRE 1296 -448 1168 -448
WIRE 1872 -448 1296 -448
WIRE 256 -432 256 -672
WIRE 352 -432 256 -432
WIRE 448 -416 416 -416
WIRE 464 -416 448 -416
WIRE 576 -400 576 -448
WIRE 1056 -400 1056 -448
WIRE 1168 -400 1168 -448
WIRE 1872 -400 1872 -448
WIRE -416 -384 -416 -480
WIRE -336 -368 -336 -400
WIRE 384 -368 384 -400
WIRE 1296 -368 1296 -448
WIRE 1328 -368 1296 -368
WIRE 1424 -368 1408 -368
WIRE 1520 -368 1504 -368
WIRE 16 -352 -144 -352
WIRE 1056 -304 1056 -320
WIRE 1168 -304 1168 -320
WIRE 1168 -304 1056 -304
WIRE 576 -288 576 -320
WIRE 1168 -288 1168 -304
WIRE 1520 -288 1520 -368
WIRE 1872 -288 1872 -320
WIRE -336 -272 -336 -304
WIRE -80 -272 -80 -304
WIRE -144 -256 -144 -352
WIRE -112 -256 -144 -256
WIRE 16 -240 16 -352
WIRE 16 -240 -48 -240
WIRE 48 -240 16 -240
WIRE 64 -240 48 -240
WIRE 256 -240 256 -432
WIRE -192 -224 -192 -400
WIRE -112 -224 -192 -224
WIRE -416 -208 -416 -304
WIRE 976 -192 880 -192
WIRE 1168 -192 1168 -224
WIRE 1168 -192 1040 -192
WIRE -192 -176 -192 -224
WIRE -192 -176 -256 -176
WIRE -80 -176 -80 -208
WIRE -192 -144 -192 -176
WIRE -256 -128 -256 -176
WIRE 1376 -112 1328 -112
WIRE 1520 -112 1520 -224
WIRE 1520 -112 1456 -112
WIRE 448 -96 384 -96
WIRE 576 -96 576 -224
WIRE 576 -96 512 -96
WIRE 880 -96 880 -192
WIRE 976 -96 880 -96
WIRE 1168 -96 1168 -192
WIRE 1168 -96 1056 -96
WIRE 1728 -96 1680 -96
WIRE 1872 -96 1872 -224
WIRE 1872 -96 1808 -96
WIRE 208 -80 160 -80
WIRE 256 -80 256 -160
WIRE 256 -80 208 -80
WIRE -256 -32 -256 -64
WIRE -192 -32 -192 -64
WIRE 160 -32 160 -80
WIRE 1328 -16 1328 -112
WIRE 1376 -16 1328 -16
WIRE 1520 -16 1520 -112
WIRE 1520 -16 1440 -16
WIRE 384 0 384 -96
WIRE 448 0 384 0
WIRE 576 0 576 -96
WIRE 576 0 528 0
WIRE 880 0 880 -96
WIRE 928 0 880 0
WIRE 1040 0 1008 0
WIRE 1168 0 1168 -96
WIRE 1168 0 1120 0
WIRE 1680 0 1680 -96
WIRE 1728 0 1680 0
WIRE 1872 0 1872 -96
WIRE 1872 0 1792 0
WIRE 256 64 256 -80
WIRE 464 96 464 80
WIRE 1408 96 1408 80
WIRE 128 112 112 112
WIRE 160 112 160 48
WIRE 160 112 128 112
WIRE 192 112 160 112
WIRE 304 112 288 112
WIRE 336 112 304 112
WIRE 384 112 384 0
WIRE 384 112 336 112
WIRE 432 112 384 112
WIRE 960 112 960 96
WIRE 1328 112 1328 -16
WIRE 1328 112 1264 112
WIRE 1376 112 1328 112
WIRE 1760 112 1760 96
WIRE 576 128 576 0
WIRE 576 128 496 128
WIRE 640 128 576 128
WIRE 672 128 640 128
WIRE 752 128 736 128
WIRE 880 128 880 0
WIRE 880 128 832 128
WIRE 928 128 880 128
WIRE 1520 128 1520 -16
WIRE 1520 128 1440 128
WIRE 1680 128 1680 0
WIRE 1680 128 1616 128
WIRE 1728 128 1680 128
WIRE 400 144 384 144
WIRE 432 144 400 144
WIRE 1168 144 1168 0
WIRE 1168 144 992 144
WIRE 1344 144 1328 144
WIRE 1376 144 1344 144
WIRE 1872 144 1872 0
WIRE 1872 144 1792 144
WIRE 640 160 640 128
WIRE 896 160 880 160
WIRE 928 160 896 160
WIRE 1264 160 1264 112
WIRE 1696 160 1680 160
WIRE 1728 160 1696 160
WIRE 1616 176 1616 128
WIRE 112 192 112 112
WIRE 192 192 112 192
WIRE 336 192 336 112
WIRE 336 192 272 192
WIRE 464 192 464 160
WIRE 1408 192 1408 160
WIRE 960 208 960 176
WIRE 1760 208 1760 176
WIRE 640 256 640 224
WIRE 1264 256 1264 240
WIRE 1264 256 640 256
WIRE 112 288 112 192
WIRE 192 288 112 288
WIRE 368 288 272 288
WIRE 1168 288 1168 144
WIRE 1168 288 448 288
WIRE 1616 288 1616 256
WIRE 1616 288 1168 288
WIRE 1920 288 1616 288
WIRE 2048 288 2000 288
WIRE 2208 288 2112 288
WIRE 2272 288 2208 288
WIRE 2272 352 2272 288
WIRE 2272 448 2272 432
FLAG 384 -480 V+
FLAG 464 80 V+
FLAG 960 96 V+
FLAG 208 -80 gate
FLAG 128 112 drn
FLAG 2272 448 0
FLAG 2208 288 output
FLAG -416 -208 0
FLAG 384 -368 0
FLAG 464 192 0
FLAG 960 208 0
FLAG -416 -480 V+
FLAG 448 -416 half
FLAG 400 144 half
FLAG -80 -176 0
FLAG -80 -304 V+
FLAG 48 -240 half
FLAG -192 -32 0
FLAG -192 -512 V+
FLAG -256 -32 0
FLAG 304 112 src
FLAG 880 -768 V+
FLAG 880 -656 0
FLAG 1056 -544 0
FLAG 1056 -848 V+
FLAG 1168 -544 0
FLAG 1408 80 V+
FLAG 1408 192 0
FLAG 1760 96 V+
FLAG 1760 208 0
FLAG -336 -272 0
FLAG -336 -400 V+
FLAG 640 -448 levelfb
FLAG 896 160 half
FLAG 1344 144 half
FLAG 1696 160 half
SYMBOL njf 192 64 M90
WINDOW 0 -37 23 VRight 2
WINDOW 3 -9 -3 VRight 2
SYMATTR InstName J1
SYMATTR Value J111
SYMBOL voltage -416 -400 R0
WINDOW 123 0 0 Left 0
WINDOW 39 10 135 Left 2
WINDOW 0 10 0 Left 2
WINDOW 3 15 104 Left 2
SYMATTR InstName V2
SYMATTR Value 36
SYMBOL schottky 1184 -224 R180
WINDOW 3 24 0 Left 2
WINDOW 0 24 64 Left 2
SYMATTR Value BAS40HY
SYMATTR InstName D2
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 176 176 M90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 2.2k
SYMBOL res 176 -48 M0
WINDOW 0 38 42 Left 2
WINDOW 3 36 66 Left 2
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL res 272 -144 R180
WINDOW 0 40 70 Left 2
WINDOW 3 45 42 Left 2
SYMATTR InstName R1
SYMATTR Value 100k
SYMBOL res 1184 -304 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R6
SYMATTR Value 470k
SYMBOL cap 352 -688 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 1000n
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0
SYMBOL res 1072 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 15k
SYMBOL res 848 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 8.2K
SYMBOL cap 1040 -208 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 10n
SYMATTR SpiceLine V=16 Irms=647m Rser=0.0322889 Lser=0 mfg="KEMET" pn="C0201C103K4PAC" type="X5R"
SYMBOL cap 736 112 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 22n
SYMATTR SpiceLine V=4 Irms=356m Rser=0.150334 Lser=0 mfg="KEMET" pn="C0402C223K7PAC" type="X5R"
SYMBOL res 544 -16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R13
SYMATTR Value 10k
SYMBOL cap 512 -112 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 22p
SYMATTR SpiceLine V=16 Irms=0 Rser=0.3482 Lser=551p mfg="Würth Elektronik" pn="885012006019 WCAP-CSGP 0603" type="NP0"
SYMBOL res 704 -688 R0
SYMATTR InstName R17
SYMATTR Value 470k
SYMBOL res 2016 272 R90
WINDOW 0 -4 57 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 600
SYMBOL res 2288 448 R180
WINDOW 0 47 75 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R8
SYMATTR Value 600
SYMBOL res -208 -384 M180
WINDOW 0 40 70 Left 2
WINDOW 3 37 41 Left 2
SYMATTR InstName R5
SYMATTR Value 100k
SYMBOL res -208 -48 M180
WINDOW 0 40 70 Left 2
WINDOW 3 38 43 Left 2
SYMATTR InstName R10
SYMATTR Value 100k
SYMBOL cap -240 -64 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C1
SYMATTR Value 10n
SYMATTR SpiceLine V=50 Irms=291m Rser=0.34258 Lser=0 mfg="KEMET" pn="C0805F103K5RAC" type="X7R"
SYMBOL cap 2112 272 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 10000n
SYMATTR SpiceLine V=25 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM188R61E106MA73" type="X5R"
SYMBOL res 1024 -16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 150k
SYMBOL res 288 272 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R15
SYMATTR Value 8.2k
SYMBOL res 1136 -16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R16
SYMATTR Value 47k
SYMBOL OpAmps\LT1058 -80 -304 R0
SYMATTR InstName U5
SYMBOL OpAmps\LT1058 384 -496 M0
SYMATTR InstName U6
SYMBOL OpAmps\LT1058 880 -784 M0
WINDOW 0 -79 26 Left 2
WINDOW 3 -120 114 Left 2
SYMATTR InstName U1
SYMBOL res 1040 -832 R0
SYMATTR InstName R19
SYMATTR Value 120k
SYMBOL res 1040 -672 R0
SYMATTR InstName R20
SYMATTR Value 91k
SYMBOL cap 1152 -576 M180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C7
SYMATTR Value 10n
SYMATTR SpiceLine V=50 Irms=291m Rser=0.34258 Lser=0 mfg="KEMET" pn="C0805F103K5RAC" type="X7R"
SYMBOL OpAmps\LT1115 464 64 R0
SYMATTR InstName U4
SYMBOL OpAmps\LT1115 960 80 R0
SYMATTR InstName U3
SYMBOL schottky 592 -224 R180
WINDOW 3 24 0 Left 2
WINDOW 0 24 64 Left 2
SYMATTR Value BAS40HY
SYMATTR InstName D1
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 592 -304 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R18
SYMATTR Value 470k
SYMBOL res 1280 144 M0
SYMATTR InstName R27
SYMATTR Value 1.5k
SYMBOL cap 1440 -32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C12
SYMATTR Value 100n
SYMBOL schottky 1536 -224 R180
WINDOW 3 24 0 Left 2
WINDOW 0 24 64 Left 2
SYMATTR Value BAS40HY
SYMATTR InstName D3
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 1408 -352 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R36
SYMATTR Value 470k
SYMBOL res 1472 -128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R29
SYMATTR Value 100k
SYMBOL cap 1792 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C18
SYMATTR Value 100n
SYMBOL schottky 1888 -224 R180
WINDOW 3 24 0 Left 2
WINDOW 0 24 64 Left 2
SYMATTR Value BAS40HY
SYMATTR InstName D4
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 1888 -304 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R38
SYMATTR Value 470k
SYMBOL res 1824 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R39
SYMATTR Value 100k
SYMBOL res 1632 160 M0
SYMATTR InstName R46
SYMATTR Value 1.5k
SYMBOL OpAmps\LT1058 1408 64 R0
SYMATTR InstName U7
SYMBOL OpAmps\LT1058 1760 80 R0
SYMATTR InstName U9
SYMBOL cap -352 -304 M180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C16
SYMATTR Value 10000n
SYMATTR SpiceLine V=25 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM188R61E106MA73" type="X5R"
SYMBOL cap 656 224 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C8
SYMATTR Value 10000n
SYMATTR SpiceLine V=25 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM188R61E106MA73" type="X5R"
SYMBOL res 1424 -384 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R22
SYMATTR Value 20k
SYMBOL res 1072 -416 M0
SYMATTR InstName R21
SYMATTR Value 7.5Meg
SYMBOL res 480 -688 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 220k
SYMBOL res 464 272 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 1.1k
TEXT -496 136 Left 2 !.tran 0 20 1m 1u uic
TEXT -496 88 Left 2 !.options plotwinsize=0 numdgt=7 method=trap
TEXT -440 -824 Left 2 ;1kHz low distortion sinewave oscillator.
TEXT -440 -792 Left 2 ;133dB. Edward Rawde 1 Feb 2025.
TEXT -432 -760 Left 2 ;Modified by Bill Sloman 1 Feb 2025.  R19 and R20 have been swapped.
TEXT -432 -728 Left 2 ;Distortion is higher, but start-up works better.